Weather ratios to predicet E.T. How do you do it?

Last time at the track I was talking to some folks that do a LOT of bracket racing and have been doing it for many years. They are never more than .001 or .002 off thier dial. After they watched me break out in the second round, we started discussing weather stations and computer programs. I told them I was thinking about getting the Crew Chief Pro program this winter. They told me that they have had 3 different programs, including Crew Chief and they don't use any of them anymore. They figure it all by hand. He told me to look in the front of the Jeg's log book and it explains ratios. He did'nt tell me whether he uses one ratio or a combination of all of them? There is Corrected Altitude, Humidity, and Wind Speed. What's the difference between Corrected altitude and Density altitude? I'm guessing that corrected altitide is some of these other factors put together? It does'nt make sense to me to use a corrected altitude ratio along with a humidity ratio? Can someone please expain this stuff to me? (remember, I'm NOT a calculus major!) Thanks!

A quick, down and dirty rule of thumb for normally asperated cars on gasoline is change of .1 in ET for every 1000 feet of DA.

I know that the ratios for everybody's car is going to be different. What I was wanting to know is, do you use just corrected altitude, or do you use a combination of all of the ratios together. It seems to me, that the Crew Chief program takes all of this info and computes it all, getting much more accurate than I can. This is why I don't understand how thay can do it so accurately by hand?

density altitude, a good weather staion does the computing for you. unless your doing class racing where you have to set up a throttle stop with out a pass it's just added info. good info grant you but knowing your car and having it tuned right is more valuable to me.

Get a weather station....
There are a few out there,,,,relatively inexpensive,,,eg TAG,,,,etc.
I have used mine for the past 2 seasons,,,and it has helped alot,,,
I dont change my car AT ALL,,,,ie,,,i dial according to the weather............
I plug in the temp, barom, humidty,,etc,,,,and it calculates the DA,,etc,,,,
I record everything in a log book,,,,
Over the past 1-2 years,,,,i can tell exactly what the car will do,,,based on the change in weather,,,,only variable is the track,,etc.
It is very helpful for eliminations as well,,,,,after a few time trials,,,,i can log the runs,,,and then pick a "dial" time,,,for eliminations,,,,as the night goes on,,and the weather changes,,,,,it is very accurate,,,at least with my car....

As far as tuning,,,it's also helpful,,,eg,,,if my car is "way off",,,and i cant explain it by the weather changes,,,i know i have a problem somewhere,,,and can start looking.......



good luck,

I've been using a Tag weather station for years...
I dont know what they want to know the corrected DA,
I want to know what the engine will see and with the
tag I can get within a few thousands but you only dial
to the hundredth

The TAG weather stations are that accurate? Looks like they are about $430 from Jegs. A couple of my buddies have the trailer mounted units with the Crew Chief Pro program and the whole setup is like $1500! Would this be a waste of a $1000?

Wow,,,,$1,000 and up ?
I am just a weekend,,bracket racer,,,few times a month,,,that got tired of losing in the first round,,,b/c i couldnt run the number,,,or know where to dial the car,,,and was just guessing....
I think a TAG,,etc,,would be OK,,,

I put a link to the system i bought,,,same one as 65Racer (Davey Boyd) on the board,,,who is a great racer,,,

http://www.ifamilysoftware.com/

I think the TAG might be a bit easier to use.....

Quote:

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The TAG weather stations are that accurate? Looks like they are about $430 from Jegs. A couple of my buddies have the trailer mounted units with the Crew Chief Pro program and the whole setup is like $1500! Would this be a waste of a $1000?

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I have the Crew Chief also... but I dont use that
anymore... I just plug my ET into the Tag(after I
save it at the starting line/ staging lanes) then
it does all the work for me. Once you establish a
data base(just a few runs) it gets more and more
accurate, plus it has 4 data bases in it... I use
them for different tracks and 1/8 mile stuff